


Whose Pup Is It Anyway?

by Destielshipper4Cas



Series: Doctor Dean [2]
Category: Supernatural
Genre: Alpha Dean, Alpha/Beta/Omega Dynamics, Alpha/Omega, Barebacking, Bottom Castiel, Doctor Dean Winchester, Explicit Sexual Content, Jealous Dean Winchester, M/M, Mpreg, Omega Castiel, Omega Verse, Possessive Dean Winchester, Pregnancy Kink, Pregnant Castiel, Pregnant Sex, Protective Dean Winchester, Smut, Top Dean, Unplanned Pregnancy
Language: English
Status: Completed
Published: 2019-09-22
Updated: 2019-10-07
Packaged: 2020-10-26 02:28:12
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 4,757
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20734751
Author URL: https://archiveofourown.org/users/Destielshipper4Cas/pseuds/Destielshipper4Cas
Summary: Dean has been miserable ever since Cas broke up with him without a convincing explanation. So, when Cas comes in for a prenatal check-up and tells him that the alpha father isn’t around, Dean thinks he might have a chance with the omega after all…





	1. Chapter 1

**Author's Note:**

> Here is the sequel to “Slick for the Doc” no one asked for. 😏 You don’t need to have read it first to understand this one, though.

Dean was in a bad mood. He had been in a bad mood a lot lately. Ever since Cas had dumped him for a reason Dean still wasn’t quite clear on.

Well, ‘dumped’ might not be quite the right word since they had never really been together in the first place, but they had been on a few dates and everything had been going great.

Or so Dean had thought. Cas apparently hadn’t agreed, which Dean had found out when the omega had mumbled his way through some sort of excuse about how he had only broken up with his alpha boyfriend a few weeks earlier and how this wasn’t the right time for him to be going out with Dean anymore.

And that had been that. No more dates. No more walking on air for Dean. He came crashing back to reality. Sam was always telling him how he confused porn with reality. Maybe he was right. Their getting together did sound like the setup of some porn he had watched. Hot sex at the practice probably didn’t make for the best foundation on which to build a relationship.

Still, try as he might, Dean could not forget about the omega—which was strange since he had only known him for a little while, and their ‘relationship’ had ended over three months ago. Cas had been a great lay, sure, but it shouldn’t be this hard for Dean to get over him.

Maybe he should get back out there. Find an omega to bury his dick in and fuck every thought of Cas out of his system. Somehow, ever since he had met Cas, no omega seemed to be doing it for Dean anymore, though.

At least he was almost done for the day. One more omega patient, then he’d be out of here and go home to wallow in self-pity with a nice bottle of beer. He should have been off work over an hour ago, but Benny was in rut, so he had to cover his patients as well.

He was about to look up the relevant information on the next patient when Anna, who probably wanted to call it a day, too, brought him in.

It was the smell that hit him first. Pregnant omega—but that wasn’t the surprising part since he was dealing with a lot of pregnant omegas here. The underlying scent, though—that was the scent that had haunted his dreams for the last thirteen weeks and six days.

He almost pulled a muscle in his neck, he looked up so fast.

There he stood, the omega of his dreams and reason for his heartache, eyes wide, staring at Dean.

Dean held the gaze for a moment before his eyes dropped to Cas’ pup bump.

He cleared his throat and said, “Thanks, Anna,” his eyes still on Cas’ rounded belly.

Cas was clearly uncomfortable, shifting his weight from one foot to the other. Once Anna had left them alone, he started, “I am actually here for Doctor Lafitte?”

Dean completely ignored his comment and said, with a touch of bitterness creeping into his voice, “Well. You certainly didn’t wait to get back out there.”

Why was he always this unprofessional where Cas was concerned?

The omega did the adorably confused frowny thing where he tilted his head when he was unsure about something and damn it! It made Dean want to go over there and kiss the frown off his face.

“What?” Cas asked.

Dean couldn’t believe that Cas didn’t even think it was weird that he had gone and gotten himself knocked up by another alpha mere _weeks_ after Dean had realized he was insanely in love with him and had wanted to do the whole wooing him and building him a nest thing.

Before Dean could clue him in that that behavior was kind of slutty of him (as the vindictive part of his brain wanted to point out), Cas continued, “Oh, no, that was… from before. I told you about my boyfriend?”

Dean ground his teeth. Yeah, the douchebag had come up in the ‘break-up talk.’

“We had… you know…” Cas blushed and Dean had to stay strong to not find that charming. “…heat sex shortly before we—” Cas motioned between Dean and himself, “—started going out.”

“So. You back together with whatshisname?”

“Balthazar,” Cas promptly replied as if Dean was interested in that jerk’s name. “And no. That’s not… He’s not in the picture anymore.”

For the first time since Cas had walked in, Dean felt his heart feel a bit lighter, as if he could breathe again (well, apart from the initial little flip-flop his heart had done when he had first seen Cas).

And just like that, instead of being mad at Cas, Dean had someone else to get mad at. “So what, he got you pregnant and then just left?!”

“It’s not a big deal,” Cas said, but his scent had turned despondent belying his words. “So, should I…” he began, motioning to the door, but Dean interrupted him because he just had to know.

“This why you broke up with me?”

Cas blinked at him, not saying anything for a moment, but Dean had waited for three _months_, he could certainly wait him out now.

Finally, Cas sighed and rubbed a hand over his face. “Come on, Dean. We were going out for a few _weeks_. That’s hardly the right time to ask you to raise a pup with me.”

“Well, you could have _told_ me at least,” Dean grumbled.

He was not ready to admit that the thought of pups had crossed his mind while they had been going out. Which had been crazy early in their relationship, granted, but Cas had triggered all sorts of alpha instincts in him. Instincts that were coming back with a vengeance now that he was seeing and smelling Cas again. He wanted to protect Cas and his pup at all costs, provide for him, make him feel safe and cared for…

The omega shrugged his shoulders awkwardly. “Now you know.”

“Now I know,” Dean repeated.

Getting together with an omega he had only met a few months earlier who was carrying another alpha’s pup would be a terrible idea. Other people would be laughing at him for even _considering _it. But this was _Cas _and Dean hadn’t felt this alive and exhilarated since he had last seen him before the break-up.

Making a split-second decision not to let Cas slip through his fingers again, he said, “So, if that was the only thing bothering you, does that mean that we can pretend the crazy pregnancy hormones didn’t make you throw away what we had, and we can pick up where we left off?”

He tried to go for a casual tone, as if he didn’t give a care in the world, but when Cas was staring at him unblinkingly, he was sure his scent had given him away anyway.

Finally, Cas asked, stunned, “You want to go out with me again?”

This time, it was Dean, who shrugged awkwardly. “Well, only if you _wanna_, obviously,” he mumbled, rubbing the back of his neck.

“With _this_?” Cas added, motioning to his knocked-up belly.

“You said douchebag wasn’t in the picture anymore, so unless you want him back…”

He didn’t get to finish that sentence because Cas was on him in a flash, kissing the living daylights out of him. It turned out, pregnant Cas tasted even better than regular Cas.

“You have no idea how horny I have been!” Cas said in-between kisses, basically trying to climb him.

Dean kissed back enthusiastically—this was all he had dreamed of these last few weeks, after all. But when Cas slipped his fingers underneath his coat, Dean caught his wrists and fended him off, ignoring Cas’ whines.

“I can’t do this in here again,” Dean explained. “Do you have any idea how long it took me to scrub this whole room clean after last time?”

He rolled his eyes when Cas began to pout. As if that would work on him… Of course, the most frustrating thing was that it _totally_ worked on him.

“Let me take you back to my place,” Dean suggested, putting a protective hand on Cas’ belly. Then he pulled him in for another kiss just because he could.

He could squeeze Cas in for the check-up tomorrow. Right now, he had a horny omega on his hands, and all he wanted to do was fuck any thoughts of the pup’s father out of Cas’ head.


	2. Chapter 2

Pregnant Cas smelled like Heaven. Dean could bury his nose in his scent gland and just go _nuts_. The omega was so ripe with pup, Dean’s dick couldn’t _wait_ to see the inside of his ass, which made for an awkward drive home—especially since Cas kept reaching over to try and unzip his pants. Dean had to slap his hand away multiple times or he wouldn’t even make it home without embarrassing himself and coming in his pants.

As soon as they had stumbled into Dean’s bedroom, Cas suddenly wasn’t as forward anymore and instead got a bit shy about undressing.

Dean helped him take off his clothes, while reassuring the omega, “Cas—I’m a doctor. I know all about the changes your body goes through. And you look sexy as hell to me.”

He didn’t just say that to put Cas at ease but was surprised to find he really meant it. He couldn’t keep his hands away from Cas’ belly, slipping underneath Cas’ shirt and fondling his pup bump.

It was even better once he had gotten rid of the rest of the omega’s clothes and could drink in the awesome sight of knocked up Cas.

The omega climbed onto the bed and presented for him, his belly heavy with pup hanging beneath him. Dean’s instincts told him to pounce and mount his omega _right this instant_, but he wanted Cas to be as comfortable as possible. So instead, he climbed on the bed, too, and turned Cas onto his side, spooning him from behind.

After all, he had to be careful with his pregnant omega. Plus, Cas had seen him about trouble slicking not too long ago, so Dean would damn well make sure the omega was slick enough instead of just pushing in.

It turned out he wouldn’t have had to worry. Cas hadn’t been kidding when he had mentioned how horny he was. Slick was basically _pouring_ out of him and Dean’s fingers slipped into his hole with ease.

“Deeeeeean,” Cas whined. “I need you.”

“I got you,” Dean rumbled, succumbing to confusing urges that made him want to fuck slow and gentle and massage Cas’ tits that weren’t as flat anymore as they had been when they had last had sex.

When he slid into his omega inch by inch, oh so careful not to hurt him, he couldn’t help but nose along his neck, searching out and then playfully mouthing along Cas’ mating gland.

He went slow and deep rather than pounding into him hard and fast, and his cock occasionally brushed up against Cas’ cervix, gently jostling the pup.

Dean reached for Cas’ rock-hard cock and gave it a few tugs, but he just couldn’t keep his hands away from his belly for too long and went back to stroking and caressing it.

He had had no idea that he was this much into pregnant sex. He had only had sex with a pregnant omega once before and it had been somewhat off-putting, the scent of another alpha’s pup nestled inside the omega making it almost impossible for Dean to keep his erection. The swollen tummy hadn’t been sexy at all, but a constant reminder that another alpha had claimed this omega.

But the scent of Cas and his belly full of pup was the _best_ aphrodisiac, leaving Dean all revved up. Still, he controlled himself and rocked into Cas at an almost leisurely pace while leaving small love bites all around Cas’ mating gland.

When Cas moaned his name, Dean brushed against the omega’s cock again, and Cas just lost it, shooting off and simultaneously clenching down on Dean’s cock, mewling out his pleasure.

Dean gave a feral roar and released his own load deep inside Cas, pushing his knot into Cas’ hole as gently as possible to lock them together in an even more intimate fashion.

The omega might be carrying another alpha’s pup, but it was Dean that brought him pleasure, it was Dean’s cock up his ass, spurting semen against his occupied womb, marking him and his pup as _Dean’s._

He had never believed alphas who talked about some imperative need to mate during sex with an omega—until now. Dean could just barely resist the temptation to sink his teeth deep into Cas’ mating gland.

“Wow,” Dean said, catching his breath, his hand still gently resting on Cas’ tummy and using it to softly pull Cas back against him so that there was no space left between them. “I forgot how hot sex with you is.”

Cas gave a nondescript grunt and put his own hands on top of Dean’s. “That’s because _you_ make it hot,” he mumbled and Dean felt him relax even more into his embrace.

Dean snuggled against the omega and placed a gentle kiss to the junction between his neck and shoulder, right where his mating gland was. He hoped that Cas knew that this hadn’t just been about getting his rocks off, but that Dean hoped to build something real here with him.

* * *

The next few days, Dean proceeded to show Cas that he was there for him and his pup. Granted, they had a lot of sex, too, but Cas was usually the one to initiate it and Dean tried to show the omega that he would make a great alpha for his little family.

Even though Cas didn’t _officially _move in with him or anything, the omega was more at his place than at his own, which was just fine with Dean because it meant he could really take care of him the way he wanted to.

Cas preferred to wait until Benny’s rut was over for the checkup because he didn’t want Dean to be too grossed out to find him sexy—which was ridiculous, of course, but Dean tried to be understanding and accommodate Cas’ strange pregnancy logic. Being patient even if their pregnant omega was being ridiculous was a desirable trait in a mate, after all.

The checkup revealed that the pup was a girl and Dean was over the moon since he had secretly hoped for that.

He had initially wanted the pup to bond with him so that she would accept him as her alpha even though she might be able to scent that they weren’t biologically related. That’s why he tried to get in some bonding time every day, talking to Cas’ belly and following Cas around so that he could caress his swollen belly and feel her kick.

Somewhere along the line, Dean himself had gotten so invested that he had gone and fallen in love with the unborn pup just like he had with her father.

Dean knew that some alphas scent-bonded with their pups even if they were still in the womb, but that’s because they were biologically related and the pup’s smell was triggering the instinctual need to protect and provide in an alpha. It was supposed to prevent alphas from just leaving their omega to raise the pups by themselves. So, that couldn’t be what was happening with him. (Dean had been lucky, though, that these instincts hadn’t been triggered in Cas’ ex and that he _had_, in fact, left Cas and the pup.)

So, Dean was left baffled as to why he couldn’t get enough of the scent and taste, always nosing along Cas’ neck, and eating him out every time before he entered him when they had sex.

It was all too good to be true. Dean was even thinking about asking Cas to mate him. Of course, Dean should have known that it really _was_ too good to be true.

He should have made sure that ‘not in the picture’ meant that the father of the pup was on the moon or something. Because just when all was going well between them and Dean was almost certain that Cas loved him back—they had to run into Cas’ ex, father of his pup, alpha to his omega, giant douchebag who could take it all away.


	3. Chapter 3

Dean and Cas had been driving around all day looking for a crib that would fit perfectly into the nursery they had somehow started setting up in Dean’s guest room without discussing it.

Cas’ nesting instincts had kicked into overdrive and the omega simply wasn’t satisfied with _any_ of the thousand cribs they had looked at.

Dean had thought it was cute at first when Cas had brought soft pillows, blankets and even stuffed animals into Dean’s bed to make it more comfortable for them. That was, until there was hardly any space for them in it anymore. Plus, Cas had raided Dean’s closet and added some of Dean’s favorite shirts to his ‘nest,’ so Dean couldn’t wear them anymore.

Dean couldn’t make fun of Cas too much, though, because he didn’t really have a better handle on his own instincts, which were, among other things, making him overprotective of his omega and pup.

He cooked for them, gave Cas footrubs and backrubs, and snarled at any alpha who happened to look at Cas’ belly and at pretty much anyone who was even _thinking_ about touching Cas.

So it was no wonder that when they literally bumped into an alpha on their way to the tenth department store of the day and the alpha steadied Cas with a hand on his arm, Dean roughly pushed him off Cas and bared his teeth.

The alpha didn’t notice or didn’t care about Dean’s possessive posturing, though, and was instead looking at Cas with wide eyes.

“Cassie?”

“Balthazar!” Cas replied, seemingly equally stunned.

Dean, meanwhile, felt as if he could throw up. So this was Balthazar. Cas’ ex and his pup daddy.

“What a nice surprise,” Balthazar said, unaware of Dean’s silent freak out. Then his eyes darted down to Cas’ belly and his hand reached out. “So, you’re…”

“Hands to yourself, dude!” Dean said, slapping his hand away before it could make contact with Cas. The other alpha clearly wanted Cas back—Dean could tell.

He was vaguely aware of Cas and Balthazar still talking, maybe Cas introducing him or something like that, but he didn’t pay attention to what they were saying.

He already saw Balthazar touch Cas, making some sort of magical instant connection with the pup, scenting Cas, scent-bonding with the pup, deciding he had made the biggest mistake of his life, then he wouldn’t want to leave, fighting for Cas and his pup, Cas would decide that he wanted to be with the biological father after all and Dean? Dean would lose the best thing of his life and all of it because…

“Dean?” Cas’ concerned voice brought him out of his spiraling thoughts.

That’s when Dean realized that he had zoned out there for a second. Balthazar was gone.

“So, that was your ex, huh? He seemed nice,” Dean tried to cover up his confusing feelings of fear and jealousy. His tone sounded clipped even to himself.

“Yes.” Cas looked away with—was that guilt? _Oh God_, he was already thinking about getting back together with his ex. “Let’s get that crib,” Cas added and briskly walked off towards the store.

Inside the store, Cas said yes to Dean’s first suggestion, which, after a series of “Are you crazy?”, “That color clashes with the wallpaper” and “That crib looks too uncomfortable” was suspicious in and on itself. A sign of guilt if Dean had ever seen one.

Dean wanted to fight for his family, make Cas see that he was the better choice here, but there was really no sense in doing that if Cas _wanted_ out. Balthazar had a right to be in his pup’s life. And Cas had a right to choose for himself who he wanted to be with. Just because it would break Dean’s heart didn’t give him the right to hold on to Cas if he didn’t want to be held on to.

On the way back, Cas kept glancing at him out of the corner of his eye. Probably thinking about how to break it to him that he wanted out. His hands were resting on his own belly and Dean wanted to cry when he thought about the fact that he might never get to know the little girl inside of Cas, waiting to be born.

Dean carried the crib inside in silence, putting it in the middle of the nursery. No sense assembling it if Cas would be taking all his stuff and move out anyway.

When he wanted to leave the nursery, Cas stood in the doorway and was looking at him, all teary eyed. Great. Here it came.

“Dean? I can’t stand you being mad at me right now. These stupid pregnancy hormones are making me all emotional and I’m just… I’m sorry, okay?”

“What’s there to be sorry about,” Dean said, unable to keep the bitterness out of his tone. He swallowed so that he would be able to force the next words out. “It’s your pup…”

The tears welled over and now Dean had a pregnant, crying omega on his hands when all he wanted to do was cry, too. But he had to be the strong alpha here, so he didn’t.

Everything in him wanted to take that last step and take his omega in his arms to console him and tell him that everything would be all right. He didn’t do that either. He wasn’t strong enough to tell Cas that he was okay with him going back to Balthazar.

“But it’s not just _my_ pup. It’s _our_ pup,” Cas said through his tears.

“I know. That’s what I meant. _Your _pup as in yours and his.” Dean had to blink a few times and open his eyes wide to make sure no tear of his own would fall down.

Cas sniffled and narrowed his eyes at him. “His?” he repeated.

He looked so miserable and confused and Dean just couldn’t fight his instincts anymore. He pulled Cas into an embrace and kissed his head, taking in the scent of distressed omega. _His_ distressed omega. And maybe—just maybe—he had a chance and all he had to do was ask.

“Please stay,” he whispered into Cas’ hair. “I know she’s going to respond better to him with him being her biological alpha, but there is no way he can love the both of you more than I do.”

Now that Cas wasn’t looking at him, Dean could let a single tear drop into Cas’ hair, and he placed another kiss on the top of Cas’ head to show him that he meant business. He would be the alpha Cas needed if only Cas would let him.

Cas started to say something, but now that he was on a roll, Dean laid all his cards on the table. “I love you,” he said, letting go of Cas just enough so that he could kiss his tears away, “and I love her.” He softly caressed Cas’ belly. “Even though I haven’t even met her yet. And I think we’d make a great family.”

Cas had stopped crying and had furrowed his brows. Maybe one of his mood swings had made him leave sadness behind and go straight to anger.

“For crying out loud, _you’re the biological alpha_!” Cas said. “I told Balthazar. You were standing right next to me.”

_What?_ Oh, right, they had jabbered on about something while Dean had tuned them out.

“I wasn’t paying attention,” Dean’s mouth explained while his mind was spinning, trying to make sense of… anything. “Wait—how is that even possible?”

“Are you really asking me that?” Cas deadpanned. “Jesus, you’re an omega doctor, you do the math. You knocked me up that very first time in the practice.”

Dean just stared at him, gobsmacked, so Cas went on, “We didn’t use protection, it was only _hours_ before I was going into heat.”

“But you were on birth control,” Dean said.

Cas rolled his eyes, but he still smelled apprehensive. “Again. You should know better than anyone else that that doesn’t always prevent pregnancy.”

It still didn’t make any sense that Dean would have been the one who had put the pup into Cas’ belly. He couldn’t help but point out, “Only less than one percent of omegas even get pregnant outside of heat.”

Cas looked at him and simply repeated, “_Hours_.”

It slowly began to sink in that he would not only get to keep Cas and the pup, but that he wouldn’t even need to worry about Balthazar deciding that he wanted his family back at all. Because it really was _Dean’s_ family.

He put a possessive hand on Cas’ belly and asked, hope blooming in his chest, “She’s mine?”

A huge smile spread across his face when he felt her kick, and he didn’t wait for Cas to answer because suddenly, everything made sense. She was his. Cas was his. _They_ were his.

“Yeah, she is,” he laughed when he felt her kick again. “I bred you up good on the first try, huh?” He patted Cas’ belly affectionately.

Cas rolled his eyes.

“Oh! I always wanted a litter, let’s try to put another one in you,” Dean suggested, which made Cas smile at long last and shake his head exasperatedly as he did whenever Dean was being silly.

“You’re ridiculous,” he said, but he was still smiling and the scent of distressed omega had been replaced by happy omega.

Still, Dean had to ask. “Why were you so distraught before if you didn’t want to break up with me?”

“Break up with you?” Cas repeated incredulously. “I thought _you_ were mad at _me _because I hadn’t told you sooner.”

“Why didn’t you?” Dean asked, too giddy that he wasn’t about to lose his family to be mad at Cas, but curious nevertheless.

Cas shrugged. “I didn’t want to tie you down. You would have stayed with me just because of the pup and I didn’t want you to come to resent us. We haven’t exactly known each other for a very long time. Aren’t you scared?”

“No, I’m not,” Dean said, staring into Cas’ eyes, trying to make him understand that he meant the world to him. “I know you’re it for me. But if you’re scared that I’ll leave you or something, I can put that mating bite on you right here, right now.”

That was not how he had imagined proposing, but on some level, he had known he would end up mating Cas when he had first asked him out. There was no question about it. Cas was his mate—it didn’t matter that they weren’t wearing each other’s mating bites yet.

“You would do that?” Cas asked.

“Of course. I’ve been thinking about it for quite a while,” Dean admitted.

“Me too,” Cas said, which made Dean grin like a loon. “And just so you know? You’re it for us, too.”

“Well then.” Dean clapped his hands and turned around to the crib. “Let me show you how good I am at providing for our pup.” He sat down on the floor and went about unpacking the different parts.

When Cas tried to sit down beside him (which was a whole process these days), Dean quickly waved him off. “Oh, no. You go sit down in that rocking chair over there and let your alpha take care of things.”

All he got for his consideration was an eye-roll from his omega. But that was okay. The fact that Cas was feeling comfortable enough calling him out on his macho alpha posturing was a good sign and made Dean love him even more.

Dean tried to reign in the smug expression when Cas did follow his instruction and sat down in the rocking chair, watching him.

Now, he better get to work because once Dean had this crib assembled, he had a romantic mating to plan…

**Notes for the Chapter:**

> I hope you liked the ending! Comments make my day! ❤️ ❤️ ❤️
> 
> And if you enjoyed it, consider **[reblogging it on tumblr](https://destielshipper4cas.tumblr.com/post/188295909374/whose-pup-is-it-anyway-finished-rating)**.


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